Printed circuit boards comprise a plurality of circuits, the density of which on the circuit boards is increasing all the time as miniaturization of electronics components continues.
Known circuit board test fixtures or apparatus can be basically divided into two classes. Belonging to the first class are fixtures having an adapter in which all circuit board test points are contacted simultaneously by means of the adapter. The second class comprises the so-called finger testers, these being fixtures which sequentially scan the individual circuit board test points by two or more finger probes.
Adapter-type test fixtures are disclosed, for example, in DE 42 37 591 A1, DE 44 06 538 A1, DE 43 23 276 A, EP 215 146 B1, and DE 38 38 413 A1.
Such adapters basically serve to adapt the irregular configuration of the circuit board test points of the board under test to a given grid pattern of the electrical test fixture. In the case of modern circuit boards to be tested, these test points are no longer arranged in a regular grid pattern, this being the reason why the contact nails producing the connection between the contact grid pattern and the circuit board test points are arranged tilted or deflecting in the adapter or a so-called translator is provided which "translates" the regular contact grid pattern into the irregular configuration of the circuit board test points.
Depending on the type of apparatus involved, the individual circuits are tested for open circuits in the circuits ("open-circuit test") and for shorts to other circuits ("short-circuit test"). The short-circuit test may involve detecting both low-impedance and high-impedance shorts.
Various test methods are known for both open-circuit and short-circuit testing, in which each circuit is tested for a short circuit or each branch of a circuit tested for an open circuit. Modern circuit boards having a large number of circuits require a corresponding large number of individual test procedures to be carried out.
Attempts have been made to optimize the individual test procedures and to minimize the number thereof, a plurality of differing methods having been proposed and put into practice for this purpose.